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參數(shù)資料
| 型號： | OPA847ID |
| 英文描述： | Wideband, Ultra-Low Noise, Voltage-Feedback |
| 中文描述： | 寬帶，超低噪聲，電壓反饋 |
| 文件頁數(shù)： | 11/23頁 |
| 文件大?。?/td> | 529K |
| 代理商： | OPA847ID |
OPA847
SBOS251C
11
www.ti.com
The high GBP and low input voltage and current noise for the
OPA847 make it an ideal wideband transimpedance ampli-
fier for low to moderate transimpedance gains. Very high
transimpedance gains (> 100k
) will benefit from the low
input noise current of a JFET input op amp such as the
OPA657. Unity-gain stability in the op amp is not required for
application as a transimpedance amplifier. Figure 3 shows
one possible transimpedance design example that would be
particularly suitable for the 155Mbit data rate of an OC-3
receiver. Designs that require high bandwidth from a large
area detector with relatively low transimpedance gain will
benefit from the low input voltage noise for the OPA847. The
amplifier’s input voltage noise is peaked up over frequency
by the diode source capacitance, and can (in many cases)
become the limiting factor to input sensitivity. The key ele-
ments to the design are the expected diode capacitance (C
D
)
with the reverse bias voltage (–V
B
) applied, the desired
transimpedance gain (R
F
), and the GBP for the OPA847
(3900MHz). With these three variables set (including the
parasitic input capacitance for the OPA847 added to C
D
), the
feedback capacitor value (C
F
) can be set to control the
frequency response.
To achieve a maximally flat 2nd-order Butterworth frequency
response, set the feedback pole as shown in Equation 1.
Equation 2 gives the approximate –3dB bandwidth that
results if C
F
is set using Equation 1.
(
)
Hz
C
R
2
GBP
π
f
D
F
dB
3
=
(2)
The example of Figure 3 gives approximately 104MHz flat
bandwidth using the 0.18pF feedback compensation capaci-
tor. This bandwidth easily supports an OC-3 receiver with
exceptional sensitivity.
If the total output noise is bandlimited to a frequency less
than the feedback pole frequency, a very simple expression
for the equivalent input noise current is shown as Equation 3.
(
)
3
F
C
2
e
R
e
R
kT
4
i
i
2
D
N
2
F
N
F
2
EQ
N
π
+
+
+
=
(3)
where:
i
EQ
= Equivalent input noise current if the output noise is
bandlimited to F < 1/(2
π
R
F
C
F
)
i
N
= Input current noise for the op amp inverting input
e
N
= Input voltage noise for the op amp
C
D
= Total Inverting Node Capacitance
f = Bandlimiting frequency in Hz (usually a post filter prior
to further signal processing)
Evaluating this expression up to the feedback pole fre-
quency at 74MHz for the circuit of Figure 3 gives an equiva-
lent input noise current of 3.0pA/
√
Hz
. This is slightly higher
than the 2.5pA/
√
Hz
input current noise for the op amp. This
total equivalent input current noise is slightly increased by
the last term in the equivalent input noise expression. It is
essential in this case to use a low-voltage noise op amp. For
example, if a slightly higher input noise voltage, but other-
wise identical, op amp were used instead of the OPA847 in
this application (say 2.0nV/
√
Hz
), the total input referred
current noise would increase to 3.7pA/
√
Hz
. Low input volt-
age noise is required for the best sensitivity in these wideband
transimpedance applications. This is often unspecified for
dedicated transimpedance amplifiers with a total output
noise for a specified source capacitance given instead. It is
the relatively high input voltage noise for those components
that cause higher than expected output noise if the source
capacitance is higher than specified.
The output DC error for the circuit of Figure 3 is minimized
by including a 12k
to ground on the noninverting input.
This reduces the contribution of input bias current errors (for
total output offset voltage) to the offset current times the
feedback resistor. To minimize the output noise contribution
of this resistor, 0.01μF and 100pF capacitors are included in
parallel. Worst-case output DC error for the circuit of Figure
3 at 25°C is:
V
os
= ±0.5mV (input offset voltage) ± 0.6uA (input offset
current) 12k
= ±7.2mV
Worst-case output offset DC drift (over the 0°C to 70°C span) is:
dV
os
/dT = ±1.5μV/°C (input offset drift) ± 2nA/°C (input
offset current drift) 12k
= ±21.5μV/°C.
D
F
F
F
C
R
GBP
π
C
R
2
1
=
π
(1)
Adding the common-mode and differential mode input ca-
pacitance (1.2 + 2.5)pF to the 1pF diode source capacitance
of Figure 3, and targeting a 12k
transimpedance gain
using the 3900MHz GBP for the OPA847 requires a feed-
back pole set to 74MHz to get a nominal Butterworth fre-
quency response design. This requires a total feedback
capacitance of 0.18pF. That total is shown in Figure 3, but
recall that typical surface-mount resistors have a parasitic
capacitance of 0.2pF, leaving no external capacitor required
for this design.
FIGURE 3. Wideband, High Sensitivity, OC-3 Transimpedance
Amplifier.
R
F
12k
12k
0.1
μ
F
100pF
Power-supply
decoupling not shown.
λ
OPA847
+5V
–5V
–V
B
C
0.18pF
1pF
Photodiode
V
DIS
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PDF描述 |
|---|---|
| OPA847 | Wideband, Ultra-Low Noise, Voltage-Feedback |
| OPA847IDBVR | Wideband, Ultra-Low Noise, Voltage-Feedback |
| OPA847IDBVT | Wideband, Ultra-Low Noise, Voltage-Feedback |
| OPA847IDR | Wideband, Ultra-Low Noise, Voltage-Feedback |
| OPAMP1EVB | Op Amp Evaluation Board Manual SOT23, SC70, and SOIC8 Package |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| OPA847IDBVR | 功能描述:高速運算放大器 Wdebnd Ult-Lo Noise Voltage Feedback RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| OPA847IDBVRG4 | 功能描述:高速運算放大器 Wdebnd Ult-Lo Noise Voltage Feedback RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| OPA847IDBVT | 功能描述:高速運算放大器 Wdebnd Ult-Lo Noise Voltage Feedback RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| OPA847IDBVT | 制造商:Texas Instruments 功能描述:OP AMP WIDEBAND VFB SOT-23-6 847 |
| OPA847IDBVT | 制造商:Texas Instruments 功能描述:Operational Amplifier (Op-Amp) IC |
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